The present invention relates to a multicast relay technique and specifically pertains to a multicast communication technique between logically independent networks.
One known technique of simultaneously sending a packet to multiple receiving devices or receivers in a network is multicast technique where a router receives a single packet and outputs duplicates of the received packet to multiple lines. The multicast technique allows for packet transmission to multiple receiving devices as destinations by utilizing a less amount of packets, compared with the unicast technique where a transmission device or a sender sends a packet multiple times to respective destinations. The multicast technique is especially suitable for real-time multimedia communication requiring high traffic, such as streaming or teleconference.
In order to allow for transmission of a multicast packet to only an authenticated user of the multicast packet, selection of an adequate line is required when a router arranged in a network outputs the multicast packet to multiple lines. PIM-SM (Protocol Independent Multicast-Sparse Mode: IETF, ‘Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification (Revised)’, RFC4601) and PIM-SSM (Protocol Independent Multicast-Source Specific Multicast) are known examples of multicast routing protocol of automatically performing optimum line selection.
As is known, for communication in each logically independent network VPN (Virtual Private Network), VRF (Virtual Routing and Forwarding) function is provided in each VPN to enable the routing protocol. The VRF technique provides an independent routing table for each VPN and is under management of a router establishing each VPN, so as to allow for communication in each VPN (IETF, ‘BGP/MPLS IP Virtual Private Networks (VPNs)’, RFC4364). In the VRF technique, multiple routers are required for management of VRFs in a distributed manner. This leads to the cost increase and the rather complicated network management. A technique has thus been proposed to allow for centralized management of multiple VRFs by one single router (AX6700S AX6300S Software Manual Ver. 11.0, Configuration Guide Vol. 3 31. Network Partition).
In a network configuration where one single router is in charge of centralized management of multiple VRFs and independently makes multicast communication in each VPN, inter-VRF communication is not allowed. A receiving device belonging to a different VPN from a VPN which a transmission device participates in is thus not allowed to receive a multicast packet from the transmission device.
With a view to receiving a multicast packet from a transmission device belonging to a different VPN from a VPN which a receiving device participates in, one proposed technique identifies the transmission device in advance and utilizes the PIM-SSM protocol to implement inter-VRF multicast routing. With a view to allowing for multicast communication between individually-operated multiple PIM-SM networks, one proposed technique utilizes MSDP (Multicast Source Discovery Protocol) to exchange transmission device information between rendezvous points of the respective PIM-SM networks (IETF, ‘Multicast Source Discovery Protocol (MSDP)’, RFC3618).
The PIM-SSM protocol technique requires previous specification of a transmission device of multicast data and is not capable of receiving multicast packets from an unspecified number of transmission devices. The MSDP technique requires settings of information on opposed rendezvous points in rendezvous points of respective VPNs and information for activating and operating the MSDP, with a view to receiving multicast data from an unspecified number of transmission devices. There is difficulty in such settings especially when multiple different networks are managed by different network administrators. The VPN network information and the VPN configuration should be shared by multiple VPNs. This may represent a breach of security in each VPN. The combined use of MSDP with PIM-SM increases the number of protocols to be managed and thereby undesirably complicates the network management.